Lignocellulosic biomass materials are renewable sources for production of amino acids for feed and food supplements, monomers and polymers for the plastic industry, and renewable sources for different types of fuels, polyol sugar substitutes (xylitol, sorbitol, manitols and the likes), and numerous other chemicals that can be synthesized from C5 and C6 sugars. Nonetheless, efficient and cost effective processes to extract C5 and C6 sugars from the biomass are still a challenge.
Classical sugar refining from corn milling comprises a sequence of resin-based ion exchangers to remove cations, anions, non-ionic compounds and color bodies. This technology has been well developed for starch hydrolysates since the 1960's and 70's and is still the method of production of sugars from corn and other easy to hydrolyze feedstocks.
It is well known that methods applied for producing 1st generation sugars, i.e., from starch or sucrose feedstocks, are too costly when applied to 2nd generation sugar production, i.e., from biomass. Biomass hydrolysis requires more severe conditions to effectively hydrolyze it as compared to starch. For example, stronger and/or more concentrated acids are used, and temperature and/or pressure of reactions are increased, all resulting in greater formation of degradation products that must be removed. Much of the increased cost is due in part to the impact of organic acids, which are an inherent component in biomass hydrolysates on the WBA resin.
The anions of biomass associated organic acids can be adsorbed by the WBA, but their adsorption is accompanied by a striking swelling of the resin, ten-fold greater than the swelling caused by mineral acid. Inherently, the resin holds a finite number of adsorption sites (e.g., the number of ammonium groups in a given volume of resin is finite), and once exhausted the resin is regenerated by: (i) washing the resin with water to recover sugar from the resin volume, yielding a “sweet water” having 2-4% sugars; (ii) periodic regeneration with mineral acid to remove the organic acid; (iii) regeneration with caustic or soda ash to prepare the resin for the next cycle; and (iv) a final wash to remove excess base. Consequently, when regenerating the resin with base, the resin shrinks. In the next adsorption cycle the resin swells again. The result of these swelling and shrinking cycles mechanically grinds the resin to dust, leading to poor mass transfer in washing, production and regeneration functions and eventually frequent need to replace the resin at high cost. When applied to refining of bagasse hemicellulose hydrolysate, the lifetime of a WBA resin is about half of that for the typical operation of refining corn sugars. Other feedstocks that release higher amounts of acetic acid in hydrolysis, such as eucalyptus, shorten the lifetime of the resin even more.